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Old 06-12-2006, 00:44   #1 (permalink)
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Fuel Pump Wiring

Gday all,
After a long time finally got the motor and box in the car, ready to run the cam in. My question is what is the proper way to wire up the fuel pump?
I want to pump to run only when the motor is running, if it stalls or anything i want the pump to stop. The pump is a mallory 140, the mallory instructions say to wire into a oil pressure switch, i've got it wired into a relay as per this;
87-Fuel pump
86-Ignition
85-Oil pressure sender
30-Battery +
Problem is that the pumps runs as soon as key is in ignition position. The oil switch is of pressure sending type, has only only one terminal. Could this be the wrong type of sender to use, by changing this to a pressure switch would it fix the problem??????
Any info helpful. Cheers
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Old 06-12-2006, 01:19   #2 (permalink)
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Re: Fuel Pump Wiring

You need a control box they use for LP gas cars. It only triggers if the engine is running. On inital start up it'll prime but thats it. Enough to fill the bowl or bowls. Once the engine runs, it detects spark and allows the pump to continue running.

The oil sender way should also work. All you do is hook up the trigger to the oil pressure sender wire. No oil pressure = no fuel pump.

[edit]Have you tried swapping 85 and 86 around? I doubt the Mallory setup would work if you have an electronic sender. IE the ones used for the dashes that tell you your oil pressure. It'd most likely only work for senders that only power an idiot light.
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Old 06-12-2006, 01:31   #3 (permalink)
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Re: Fuel Pump Wiring

there are simple relays that switch using rpm as a reference... I can't remember the name of them but i tried to use one with mine and it didn't like the msd coil wire high voltage...

I just ran the pump direct for now until i go into the cabin and tap into the tach wire of the 6AL...
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Old 06-12-2006, 01:36   #4 (permalink)
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Re: Fuel Pump Wiring

When i had the ute, it had the gas cut off control box. Didn't keep it with the sedan. I got tomorrow off, so going go see how much it will be too put a tee piece and pressure switch in is. Only other thing is what pressure rating should the switch be, the ones i've found are 4psi, 6-8psi, 15psi etc, which would be the best to use??
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Old 06-12-2006, 01:41   #5 (permalink)
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Re: Fuel Pump Wiring

Just tried to swap 85 and 86 around, still did the same thing, will have to look at trying on of the pressure switch types.
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Old 06-13-2006, 01:09   #6 (permalink)
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Re: Fuel Pump Wiring

here is what you need made by MSD, I will try one of these soon...
cheers


http://www.msdignition.com/pdf/FRM23778-PN%208950.pdf
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Old 06-13-2006, 05:35   #7 (permalink)
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Re: Fuel Pump Wiring

The way you have wired it up is working in reverse as you know. Does it turn off after the engine has started?

This is because the oil pressure switch is closed before you start the car (indicating NO pressure) which would normally turn on your red dash light on (but at the moment, turns your pump on). After you start the engine and the oil pressure rises, the oil sender switch opens which turns the light out, and in your case, probably turn the pump off.

Swapping 85 & 86 does nothing (unless there's a diode in the relay).

Mr Gasket makes an oil pressure switch that should work for you. The starter relay wiring allows the pump to come on as you momentarily turn the key to start too.

http://www.jegs.com/webapp/wcs/store...tegoryId=12855

http://go.mrgasket.com/pdf/7872.pdf
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Old 06-13-2006, 06:09   #8 (permalink)
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Re: Fuel Pump Wiring

Here's another Holley one.

Activated BY oil pressure, not lack of it.

http://www.jegs.com/webapp/wcs/store...tegoryId=12689



I've tried nutting out how you could wire up your current switch with a reverse contact 5 pin relay, but you always need 12V power to ironically "turn it off", so that's no good in an accident.
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Old 06-13-2006, 06:27   #9 (permalink)
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Re: Fuel Pump Wiring

Those switches look great, going to speak to my local superplus tomorrow see if they got any, if not order one.
SO by using one of these switches what is the correct way to wire the fuel pump up then?
Cheers
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Old 06-13-2006, 07:37   #10 (permalink)
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Re: Fuel Pump Wiring

Having just looked at my Comp140 instructions, they are identical in the wiring diagram I've attached below from the Mr Gasket website.

Here's a better view of the Holley switch.


Mr Gasket switch


Instructions
http://go.mrgasket.com/pdf/7872.pdf

There's one common terminal which goes to the pump. Then one of the adjacent terminals is normally open and the other normally closed (with engine off). Connect a 12V wire from the starter motor solenoid to the normally closed terminal and your 12V ignition wire to the normally open terminal. Only when you crank your engine will the pump come on, then as it fires and the pressure gets above 15psi, the normally open switch closes and keeps it running until you turn the motor off.

If you want to keep your standard pressure switch for the dash red light, then simply fit a t-piece into the top of your engine and use both switches.

Good luck!
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